The broad objective is to better understand the roles played by vestibular and other sensory inputs in controlling gaze, head posture and overall balance. This includes (a) characterizing the interaction among sensory input signals and their transformation by the central nervous system, (b) identifying the structural components and pathways of the CNS which are involved, and (c) defining the adaptive (or mal-adaptive) strategies used by normal subjects in an altered gravity environment and by subjects with a peripheral vestibular deficit or CNS pathology. The specific aims are to (1) describe the influence of gravity and changes in support surface compliance on balance and head posture in normal human subjects, in those with a bilateral peripheral vestibular deficit, and in those with spasmodic torticollis, (2) map the brainstem and cerebellum during visual (optokinetic) stimulation using magnetic resonance imaging, and (3) develop a distributed parallel neural network for the vestibulo-ocular reflex (VOR) in 3-dimensions which incorporates spatial and temporal characteristics of single neurons and a physiological mechanism for adaptation.